1. Field of the Invention
The present invention relates to a 4-cycle engine, particularly, an improvement in a 4-cycle engine including an engine body which is comprised of a crankcase having first and second bearing portions for supporting opposite ends of a crankshaft, and a head-integral type cylinder barrel having a cylinder bore with a piston received therein.
2. Description of the Related Art
It is known, as disclosed, for example, in Japanese Patent Application Laid-open No. 8-177441, that in a 4-cycle engine of the mentioned type, the crankcase is comprised of first and second case halves which are coupled to each other at a parting plane extending to obliquely intersect the axis of the first and second bearing portions. The cylinder barrel and the first bearing portion are formed by being integrally molded on the first case half. The second bearing half is formed by being integrally molded on the second case half.
In this type of engine, it is effective to reduce the distance as much as possible between the first and second bearing portions for supporting the opposite ends of the crankshaft, in order to alleviate the bending moment generated on the crankshaft by a load applied from the piston to the crankshaft to enhance the durability of the crankshaft.
In the above conventional engine, however, a valve operating mechanism connected to the crankshaft is disposed adjacent the inside of the second case half. For this reason, when the distance between the first and second bearing portions is to be reduced, the valve operating mechanism is an obstacle. Namely, at least one of the bearing portions cannot be disposed adjacent a crank portion of the crankshaft, because it is hindered by the valve operating mechanism. When the engine is to be assembled, a portion of the valve operating mechanism is obliged to be temporarily assembled to the crankshaft before coupling the first and second case halves to each other. Hence, it cannot be said that assembling this type of engine is easy is good.